The need for preventing inadvertent needle sticks has been recognized for many years. For example, U.S. Pat. No. 2,571,653 to Bastien shows a syringe in which the barrel of the syringe is mounted within a protective sheath. The sheath can be placed at different axial positions relative to the barrel, one exposing the needle for use and one covering the needle for safety. Many other safety syringe assemblies have been developed as well. However, one of the problems with the prior art safety syringe assemblies is that they generally cannot be used with conventional syringes, are awkward to use and make calibrations and volume graduations difficult to see clearly. Also, existing safety syringe assemblies often are to economical to produce; this is especially true when the syringe structures are intended to be disposable.